1. Field of the Invention
The present invention relates to a fuel injector for use in an internal combustion engine, and more particularly, relates to a fuel injector by which fuel is atomized and injected under a relatively low pressure directly into the combustion chamber of a two-stroke engine.
2. Description of the Related Art
A fuel injector for use in an internal combustion engine has a construction such that it is able to inject a required correct amount of fuel even when a minimum required amount of fuel is to be injected. The required amount of fuel to be injected however, changes considerably in accordance with a change in the operating state of the engine, and therefore, particularly where a low pressure fuel injector is used, when the required amount of fuel to be injected is increased, the injection time of the fuel injector becomes considerably longer. Nevertheless, for example, in a two-stroke engine, the injecting operation of the fuel must be completed within a short time, and therefore, where a low pressure fuel injector is used in a two-stroke engine, it is difficult to inject a necessary amount fuel over the entire range of from the minimum required amount to the maximum required amount.
Therefore, where the injecting operation must be completed within a short time, usually separate fuel injectors for a small amount of fuel and fuel injector for a large amount of fuel are provided. Namely, when the required amount of fuel is small, fuel is fed from the fuel injector for the small amount of fuel, and when the required amount of fuel is large, additional fuel is fed from the fuel injector for the large amount of fuel (see Japanese Examined Patent Publication No. 61-5543).
Nevertheless, as well known to a person skilled in the art, in practice it is often difficult to arrange two injectors in a combustion chamber and the like, in view of the space limitations involved.
In another known fuel injector, a valve lift control means comprising a spring (referred to as a delay spring) is provided, to thereby expand the controllable range of the amount of fuel injected by the fuel injector and correctly control the amount of fuel injected by the fuel injector. This delay spring is arranged between the needle and the movable core, and when the movable core is attracted by the energized exciting coil, the attracting force for the movable coil is accumulated in the delay spring for a predetermined time. Thereafter, the attracting force thus accumulated is added to the attracting force caused by the exciting coil, and these attracting forces are transmitted to the needle (see Japanese Unexamined Utility Model Publication No. 58-72455).
Even if such delay spring is used, however, it is difficult to expand the controllable range of the amount of fuel injection over the wide range of from a small amount to a large amount, and to carry out a fine adjustment of the amount of fuel injected.